KABUL -- Several people have been killed in three explosions in Kabul near the funeral of an Afghan senator's son, one of five victims of deadly clashes between police and protesters a day earlier, witnesses and officials say.

Waheed Majroh, a spokesman for the Afghan Health Ministry, told RFE/RL that at least six people were killed and 87 others injured in the blasts, which Afghan Chief Executive Officer Abdullah Abdullah said were the work of suicide bombers.

Abdullah was one of several senior government officials attending the funeral at the time of the explosions, though he was unharmed.

He said on state television afterward that three suicide bombers detonated their vests as mourners were paying their respects to Salem Izadyar, the son of a senator who was killed during a protest on June 2 attended by hundreds in Kabul.

The office of President Ashraf Ghani said in a statement after the deadly blasts that the country was "under attack."

There were conflicting reports of the death toll throughout the day.

Interior Ministry spokesman Najib Danish said that "initial reports show at least 10 casualties" from the three blasts that rocked the cemetery where Izadyar, the son of senator Alam Izadyar, was about to be buried.

Alam Izadyar is deputy speaker for the upper house of the country's parliament.

A report by Germany's dpa news agency citing an unidentified security official put the death toll at 20 people, with 18 people wounded.

The blasts at Izadyar's funeral came as Afghan authorities pledged to investigate the violent clashes during an antigovernment protest on June 2 in response to this week's devastating truck-bomb attack in Kabul.

Deputy Interior Minister Murad Ali Murad said on June 3 the attorney general would investigate allegations of violence on June 2 by police as well as by demonstrators, some of whom appeared to be armed.

The June 2 rally descended into hours of confrontation between stone-throwing protesters and police, who fired into the air to repel crowds trying to reach the presidential palace by pushing through security cordons.

The protest followed a massive truck-bomb explosion on May 31 that killed at least 90 people and wounded 460 -- one of the deadliest attacks seen in the Afghan capital since the U.S.-led campaign that toppled the Islamist Taliban regime in 2001.

The attack mounted additional pressure on President Ashraf Ghani's government over its inability to ensure security in Kabul.

Streets in the center of the Afghan capital were closed on June 3 as the authorities tried to prevent a repeat of the violence.

However, a group of about 200 protesters remained near the blast site in the center, sheltering from the sun in open tents.

Intelligence officials have blamed the attack on the Taliban-affiliated Haqqani network, a group that has been linked to several similar attacks in the past.

The Taliban has denied being behind the attack, but media reports say that the president has signed orders to execute 11 Taliban and affiliated Haqqani network militants on death row, despite that denial.

The militant group on June 2 threatened retaliation if the Afghan government executed Taliban prisoners in revenge for the attack.

In a statement on its website, the Taliban said that "harsh exemplary attacks" would follow, including the killing of foreign hostages it holds, if the government executed the 11 prisoners.

The latest violence comes as U.S. and coalition officials are working on plans expected to see an increase of between 3,000 and 5,000 in the number of foreign troops in Afghanistan.

The huge truck-bomb attack was the latest in a long series of high-profile militant attacks that have killed hundreds of civilians in Afghanistan since most international forces left the country in 2014.

In the first three months of the year at least 715 civilians were killed across the country, after almost 3,500 last year -- the deadliest on record for Afghan civilians.